1. Field of Invention
The present invention generally relates to a method of driving a matrix type display apparatus which suppresses an occurrence of degradation in quality of picture and which reduces the power consumption to an extremely low value, and to such a matrix type display apparatus and electronic equipment.
2. Description of Related Art
In display apparatuses used in portable electronic equipment, such as a hand-portable telephone set, the number of display dots has increased year after year so that more information can be displayed on the screen thereof. On the other hand, the portable electronic equipment is battery driven in principle, and thus required to reduce the power consumption thereof as much as possible. Therefore, the display apparatus used in the portable type electronic equipment is required to have two apparently contradictory features, that is, high resolution and low power consumption. Thus, to solve such a problem, an attempt has been made to adapt the display apparatus to perform a full-screen display operation when a high resolution is required, and to display only a partial region of the screen thereof and put the remaining region into a non-display state.
However, there has occurred a problem that power consumption is ineffectively reduced against all expectation even when only a partial region of the screen of a display apparatus is indicated in the case that a high resolution is not required. Further, the configuring of the display apparatus in such a way as to display only a part of the screen thereof and to put the remaining region of the screen thereof into a non-display state causes another problem in that the circuit of the apparatus is complex.
The present invention is accomplished in view of the aforementioned problems. An object of the present invention is to provide a method of driving a matrix type display apparatus, which can suppress an occurrence of degradation in the quality of picture, enhance the resolution thereof and reduce the power consumption thereof, and simplify the configuration thereof, and to provide a matrix type display apparatus having a driving circuit for performing this a method and to provide electronic equipment having this display apparatus.
To resolve such problems, according to an aspect of the present invention, there is provided a method of driving a pixel provided corresponding to each of intersections between a plurality of scanning lines and a plurality of data lines by a switching device, wherein when only a first region including a part of the plurality of scanning lines is put into a display state while a second region including the rest of the plurality of scanning lines is put into a non-display state, a non-selection signal, in response to which the switching device is brought into a non-conducting state, is supplied to each of the scanning lines of the second region by inverting a polarity of a signal voltage every one or more vertical scanning time period, by using an intermediate value which is represented by the signal supplied to the data lines as a reference.
It is desirable only from the viewpoint of low power consumption that a signal representing the intermediate value of values represented by signals to be supplied to the data lines is supplied to each of the scanning lines belonging to the second region serving as a non-display region. However, with this configuration, it is necessary to additionally select a signal representing a voltage which corresponds to the intermediate value. Thus, the configurations of the voltage generating circuit and the scanning line driving circuit are complex.
In contrast with this, according to the present invention, the non-selection signal is supplied to each of the scanning lines of the second region by inverting the polarity every one or more vertical scanning time periods, on the basis of the intermediate value. Thus, the effective value of the voltage becomes nearly zero. There is no need for generating and selecting a signal representing the voltage which corresponds to the intermediate value. Consequently, the configuration of the circuit is simplified. Furthermore, the voltage level is changed every one or more vertical scanning time periods, more preferably, every time period, which is longer than the vertical scanning time period. Thus, the frequency of the signal supplied to the scanning line is reduced. Consequently, the power consumption resulting from the voltage level changing operation in the circuit for driving the scanning lines is suppressed. Moreover, the power consumption resulting from the charging and discharging of the associated capacity of the scanning lines and the driving circuit is also suppressed.
Further, according to the present invention, preferably, a selection signal, which puts the switching device into a conducting state, is supplied in one of time periods into which a horizontal scanning time period is divided, and a non-selection signal, which puts the switching device into a non-conducting state, is supplied in the remaining ones of the time periods by inverting the polarity of a signal voltage every predetermined time period, by using the intermediate value which is represented by the signal supplied to the data line as a reference. With this configuration, the signal supplied to each of the scanning lines of the first region used as the display region is not different from a signal in an ordinary state in which all the scanning lines are in the display region. This prevents the configuration of the circuit from being complex by changing the duty ratio. Moreover, this prevents the quality of display of the first region from being deteriorated in comparison with that in the ordinary state.
Furthermore, according to the present invention, preferably, the selection signal is supplied to each of the scanning lines before the second region is put into a non-display state. As described above, each of the pixels of the present invention is driven by the switching device. Thus, in the case that a certain one of the pixels is in the second region, the previously written charge is held as it is according to the non-conducting state of the switching device. Consequently, in the case of a transition from the ordinary state, in which the region including all the scanning lines is used as the display region, to the state in which the second region is put into the non-display region, preferably, the apparatus performs a step at which all the pixels included in the second region are once put into an off display condition. The present invention enables the method to include this step.
Further, to achieve the foregoing object, there is provided a method of driving a matrix type display apparatus for driving a pixel provided corresponding to each of intersections between a plurality of scanning lines and a plurality of data lines by a switching device, wherein in the case that only a first region including a part of the plurality of scanning lines is put into a display state while a second region including the rest of the plurality of scanning lines is put into a non-display state, when a scanning line in the second region is selected, a signal having a positive-side voltage level and a negative-side voltage level, which are determined by using an intermediate value represented by a signal to be supplied to the data lines as a reference, is supplied to each of the scanning lines by inverting a polarity of a signal voltage every one or more vertical scanning time period, by using the intermediate value as a reference.
Only from the viewpoint of limiting the power consumption of each of the data lines at the time of selecting the scanning lines of the second region, which is a non-display region, to a low value, it is preferable that a signal representing the intermediate value of the positive-side voltage level value and the negative-side voltage level value is supplied to each of the data lines. However, with this configuration, it is necessary to additionally select a signal representing a voltage which corresponds to the intermediate value, in addition to the positive-side voltage level and the negative-side voltage level. Thus, the configurations of the voltage generating circuit and the scanning line driving circuit are complex.
In contrast with this, according to the present invention, the signal having the positive-side voltage level and the negative-side voltage level is supplied to each of the data lines at the time of selecting the scanning lines of the second region by inverting the polarity every one or more vertical scanning time periods, on the basis of the intermediate value. Thus, the effective value of the voltage becomes nearly zero. There is no need for generating and selecting a signal representing the voltage which corresponds to the intermediate value. Consequently, the configuration of the circuit is simplified. Furthermore, it is sufficient to configure the apparatus so that the voltage level of the voltage to be supplied to the data lines is switched every longer period by inverting the polarity every one or more horizontal scanning time periods, more preferably, every time period, which is longer than the horizontal scanning time period. Thus, the frequency at which the data lines are driven is reduced. Consequently, the power consumption resulting from the voltage level changing operation in the circuit for driving the data lines is suppressed. Moreover, the power consumption resulting from the charging and discharging of the associated capacitance of the circuit and the wirings is also suppressed.
Incidentally, according to the present invention, it is preferable that the polarity inverting period of the positive-side voltage level and the negative-side voltage level at the time of selecting the scanning lines of the second region is a time period whose length is obtained by multiplying the length of the horizontal scanning time period by a value approximately equal to a quotient of the number of the scanning lines of the second region by an integer that is equal to or larger than 2. Thus, when the scanning line of the second region is selected, the time period in which the signal having the positive-side voltage level is supplied is equal in length to the time period in which the signal having the negative-side voltage level is supplied, even during the time period during which the second region is in a non-display state. The effective voltage applied to the pixel put into a non-display state is uniformed in such a manner as to have a value of nearly zero. Incidentally, in the apparatus of the present invention, the length of the polarity-inverting period is maximized by being set at a value that is obtained by multiplying the horizontal scanning time period by a quotient of the number of the scanning lines of the second region by 2. Consequently, the power consumption resulting from the voltage level changing operation in the circuit for driving the data lines is suppressed. Moreover, the power consumption resulting from the charging and discharging of the associated capacity of the circuit and the wirings is also suppressed.
Further, according to the present invention, it is preferable that when the scanning line of the first region is selected, signals relatively having the positive-side voltage level and the negative-side voltage level are alternately supplied to each of the data lines in a time period in which a selection signal putting the switching device into a conducting state is supplied, and a time period in which a non-selection signal putting the switching device into a non-conducting state is supplied, of one horizontal scanning time period correspondingly to the polarity of a voltage represented by the selection signal which is determined by using the intermediate value as a reference. More preferably, the time period in which the signal having the positive-side voltage level is supplied is nearly equal in length to the time period in which the signal having the negative-side voltage level is supplied. With this configuration, when the scanning line of the first region serving as a display region is selected, signals relatively having the positive-side voltage level and the negative-side voltage level are alternately supplied in the time period during which the selection signal is supplied, and the time period during which the non-selection signal is supplied within a horizontal scanning time period, regardless of what pattern is displayed therein. The effective values of the voltages applied to the pixels put in the display state in a holding time period are nearly equal to one another. This prevents an occurrence of a problem that the effective value of the voltage varies according to a change in turning-off leakage current in the holding time period. Consequently, the degradation in quality of picture can be prevented.
Meanwhile, according to the present invention, it is preferable that when the scanning line of the second region is selected before the second region is put into a non-display state, a signal for putting the second region into an off display condition is supplied thereto. As described above, each of the pixels of the present invention is driven by the switching device. Thus, in the case that a certain one of the pixels is in the second region, the previously written charge is held as it is, according to the non-conducting state of the switching device. Consequently, in the case of a transition from the ordinary state in which the region including all the scanning lines is used as the display region, to the state in which the second region is put into the non-display region, preferably, the apparatus performs a step at which all the pixels included in the second region are once put into an off display condition. Thus, the second region can be more reliably put into the non-display state.
Moreover, to achieve the aforementioned object, there is provided a matrix type display apparatus for driving a pixel provided corresponding to each of intersections between a plurality of scanning lines and a plurality of data lines by a switching device. This matrix type display apparatus may include a scanning line driving circuit for supplying a selection signal in response to which the switching device is put into a conducting state, in one of time periods to which a horizontal scanning time period is divided, and a non-selection signal in response to which the switching device is brought into a non-conducting state, in the remaining time periods to each of the scanning lines of the second region by inverting a polarity of a signal voltage every predetermined time period, by using an intermediate value which is represented by the signal supplied to said data lines as a reference, when only a first region including a part of the plurality of scanning lines is put into a display state while a second region including the rest of the plurality of scanning lines is put into a non-display state , and for supplying the non-selection signal to each of the scanning lines of the second region by inverting a polarity of a signal voltage every one or more vertical scanning time period, by using the intermediate value which is represented bythe signal supplied to the data lines as a reference, and a data line driving circuit for alternately supplying, when the scanning line of the first region is selected, signals relatively having a positive-side voltage level and a negative-side voltage level, which are determined by using the intermediate value as a reference, in a time period in which the selection signal is supplied, and a time period in which the non-selection signal is supplied, of a horizontal scanning time period correspondingly to a polarity of a voltage represented by the selection signal which is determined by using the intermediate value as a reference, and for supplying, when the scanning line of the second region is selected, the signals relatively having the positive-side voltage level and the negative positive level, which are determined by using the intermediate value as a reference, by inverting the polarity of a signal voltage every one or more horizontal scanning time periods.
The aforementioned effects can be obtained at both the scanning line side and the data line side of the apparatus of the present invention. Therefore, owing to the synergistic effects thereof, the power consumption can be reduced still more. Further, the apparatus of the present invention can prevent an occurrence of degradation in the quality of picture, and enhance the resolution thereof, and simplify the configuration thereof.
Incidentally, according to the present invention, preferably, the scanning line driving circuit alternately inverts the polarities of the voltages represented by the selection signals respectively supplied to adjacent ones of said scanning lines. The current-voltage characteristic of the switching device for driving the pixels in the case of applying a positive-side voltage is slightly different from that of the switching device in the case of applying a negative-side voltage. Thus, the voltage applied to the pixel may vary. However, according to the present invention, the polarity of the selection signal voltage supplied to the adjacent scanning lines is inverted. Moreover, the polarity of the data signal voltage corresponds to the polarity of the selection signal voltage, so that the voltage applied to the pixel placed on the even-numbered scanning line and the voltage applied to the pixel placed on the odd-numbered scanning line are alternately inverted in polarity. Therefore, the display unevenness among the pixels is inconspicuous. Further, the polarity inversion driving frequency is high so that flicker is inconspicuous.
Furthermore, according to the present invention, preferably, the scanning line driving circuit supplies the selection signal to each of the scanning lines before the second region is put into a non-display state. Further, when the scanning line of the second region is selected, the data line driving circuit supplies a signal putting the second region into an off display condition. With this configuration, as described above, in the case of a transition from the ordinary state in which the region including all the scanning lines is used as the display region, to the state in which the second region is put into the non-display region, all the pixels included in the second region are once put into an off display condition. Thus, the second region can be more reliably put into the non-display state.
Meanwhile, according to the present invention, preferably, the data line driving circuit has a memory for storing display data to be respectively displayed at the pixels. When the scanning line of the first region is selected, the data line driving circuit reads the display data from the memory and generates signals respectively having the positive-side voltage level and the negative-side voltage level according to the display data. When the scanning line of the second region is selected, the data line driving circuit stops reading display data from the memory. With this configuration, when the scanning line of the second region is selected, there is no need for displaying display data. According to the present invention, in such a case, the reading of the memory is stopped. Thus, an increase in the power consumption is suppressed. Consequently, the power consumption is reduced still more.
Furthermore, according to the present invention, preferably, the matrix type display apparatus may further include a gray scale level control signal generating circuit for generating a gray scale level control signal. Further, preferably, when the scanning line of the first region is selected, the data line driving circuit supplies display data to pixels placed on the scanning line by modulating the display data so that the modulated display data corresponds to a gray scale level at which data is displayed, at each of the pixels, according to timing provided by the gray scale level control signal. Moreover, preferably, when the scanning line of the second region is selected, the gray scale level control signal generating circuit stops generating a gray scale level control signal, and the data line driving circuit stops modulating the display data. With this configuration, in the case that there is no need for displaying the data, the generation of the gray scale level control signal is stopped. Furthermore, an operation of modulating a signal corresponding to a gray scale level is stopped. Thus, the power consumption is reduced still more.
Further, according to the present invention, preferably, the switching device is a two-terminal switching device. Moreover, preferably, an electro-optical material is sandwiched between a pair of substrates. Furthermore, preferably, each of the pixels is constituted by series-connecting the two-terminal switching device and the electro-optical material between the plurality of scanning lines provided on one of the pair of substrates and the plurality of data lines. The apparatus of the present invention may use a three-terminal device, for instance, a transistor, as the switching device. However, there is the necessity for forming the scanning lines and the data lines in such a way as to intersect one another on one of the substrates. Thus, such an apparatus has a defect in that the likelihood of an occurrence of a short circuit in the wiring is enhanced. Moreover, the manufacturing process is complexed. In contrast, when the two-terminal switching device is used, the scanning lines are formed on one of the substrates, while the data lines are formed on the other substrate. Thus, the apparatus of this configuration has an advantage in that no short circuits are caused in the wiring in principle. Further, the manufacturing process can be simplified as compared with that in the case of using the three-terminal switching device.
Furthermore, according to the present invention, preferably, the twoterminal switching device has a conductor/insulator/conductor structure connected to the scanning line or the data line. The conductor, which is the first layer, can be used as the scanning line or the data line, without any change. Further, the insulator is formed by anodizing this conductor, that is, the first layer. Consequently, the manufacturing process is simplified still more.
Additionally, to achieve the object, there is provided electronic equipment that may include the aforementioned matrix type display apparatus. Therefore, as described above, this electronic equipment can prevent an occurrence of degradation in the quality of picture, and enhance the resolution thereof, and simplify the configuration thereof.